Chief Inspector Angus MacInnes, from Police Scotland, said: "The fourth person was recovered from the wreckage a short time ago and we have deployed family liaison officers to support those who have lost loved ones. We are also working with the industry to help support all of those affected."

The helicopter was being operated by CHC for oil company Total and was transporting workers from the Borgsten Dolphin platform when it is believed to have experienced a "catastrophic" loss of power as it approached Sumburgh airport on the southern tip of Shetland's main island at around 6.20pm.

A major rescue mission was launched and 14 survivors were taken to hospital in Shetland, where two workers are still being cared for.

Tributes have been paid to the three men and one woman killed, named as Duncan Munro, 46, from Bishop Auckland, County Durham; George Allison, 57, from Winchester, Hampshire; Sarah Darnley, 45, from Elgin in the Highlands; and 59-year-old Gary McCrossan, from Inverness.

The wreckage remained at sea tonight but it is understood it will be brought ashore for inspection by a team from the Air Accidents Investigation Branch (AAIB).

Shetland coastguard manager John Webster told the Press Association earlier: "The heavy-lift ship is out at the moment trying to recover what wreckage it can from the sea.

"After that the Air Accidents Investigation Branch will decide where to take it.

"A lot of our crew are shocked, to say the least. We've dealt with a few air crashes before. Each one is different but each is as sad as the last."

Mr Webster said of the moment he was alerted to the crash: "We got a call from the ARCC (Aeronautical Rescue Coordination Centre) to say that an inbound helibus had disappeared off the radar.

"That was the first indication that we had that something serious had happened, and we mobilised our helicopters, ground teams and lifeboats to the last known position.

"Of course when the units got near the position they saw the wreckage of the helicopter, which was actually upside down at the time."

All Super Puma flights to and from UK offshore installations have meanwhile been suspended.

Helicopter operator CHC has grounded the AS332 L2 aircraft - the model involved in the crash - and suspended all UK commercial flights of three other Super Puma types.

It follows a recommendation by the offshore industry's Helicopter Safety Steering Group (HSSG) which urged the precautionary measure until there is "sufficient factual information" to resume flights.

The HSSG is made up of representatives from oil and gas firms, contractors, helicopter operators, offshore unions, the Health and Safety Executive (HSE) and the Civil Aviation Authority (CAA).

The group met in Aberdeen yesterday and recommended the temporary suspension of all Super Puma commercial passenger flights to and from the UK's oil and gas installations.

This includes the AS332 L, L1, L2 and EC225 models.

CHC said it was "devastated" by the accident and would follow the recommendation, which allows for the operation of emergency rescue flights.

Bristow said three flights scheduled for today had been cancelled and further updates would be issued in due course.

The HSSG will meet again on Wednesday to review the suspension unless "any significant information comes to light before this date".

Industry body Oil & Gas UK has meanwhile arranged a meeting of operators and major contractors tomorrow to discuss ways of minimising the impact of the grounding of flights on the offshore workforce.

Scotland's Finance Secretary John Swinney said the government did not anticipate that the temporary suspension would have any immediate impact on the production of oil and gas in the North Sea but that the situation would be closely monitored.

The four people killed in the crash were all working for contractors.

Mr Munro leaves behind wife Penny and 12-year-old daughter Katie.

His family said in a statement: "He will be sadly missed by everyone that knew him and his death will leave a large void in a lot of people's lives."

Ms Darnley's family paid tribute to a "fun-loving, free spirit" who was brought up in Elgin and moved to Aberdeen aged 19.

The offshore worker is survived by parents Anne and Edmund Darnley, her sister Angela and nephew Nicholas.

Her mother Anne said: "We are shocked by the sudden loss of Sarah, who was a fun-loving, free spirit who will be sorely missed.

"Sarah lived life to the full, she was easygoing and a one-off. She will be deeply missed by all who knew her."

Mr McCrossan worked for Stork Technical Services. Mike Mann, a senior vice president at the firm, said: "Our heartfelt condolences go out to Gary's family and to all of those affected by this tragedy."

Mr Allison had been working at the Offshore Dunbar Platform as a project safety supervisor for just over a year when he was killed, according to his LinkedIn profile.

He described himself as a "highly qualified, experienced and competent Safety Advisor" who has worked in the offshore industry for 27 years.

There have been five North Sea incidents involving Super Pumas since 2009. In April that year an AS332 L2, this time operated by Bond, went down north east of Peterhead on its return from a BP platform, killing all 14 passengers and two crew on board.

Pat Rafferty, Scottish secretary of the Unite union, said: ''This is the fifth major incident in the last four years involving Super Puma helicopters in the UK offshore industry and the second resulting in fatalities. It's unacceptable and it can't go on."

Super Puma manufacturers Eurocopter said the company was "supporting CHC and relevant authorities with their investigations".